Changes in Pelvic Incidence, Pelvic Tilt, and Sacral Slope in Situations of Pelvic Rotation.

STUDY DESIGN: Digitally reconstructed radiograph-based study. OBJECTIVE: Using a computer-based method to determine what degree of pelvic rotation is acceptable for measuring the pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS). The effectiveness of a geometrical formula used to calculate the angle of pelvic rotation proposed in a previous article was assessed. SUMMARY OF BACKGROUND DATA: It is unclear whether PI, PT, and SS are valid with pelvic rotation while acquiring a radiograph. MATERIALS AND METHODS: Ten 3-dimensionally reconstructed models were established with software and placed in a neutral orientation to orient all of the bones in a standing position. Next, 140 digitally reconstructed radiographs were obtained by rotating the models around the longitudinal axis of each pelvis in the software from 0 to 30 degrees at 2.5-degree intervals. PI, PT, and SS were measured. The rotation angle was considered to be acceptable when the change in the measured angle (compared with the "correct" position) was <6 degrees. The rotation angle (α) on the images was calculated by a geometrical formula. Consistency between the measured value and the set angle was assessed. RESULTS: The acceptable maximum angle of rotation for reliable measurements of PI was 17.5 degrees, and the changes in PT and SS were within an acceptable range (<6 degrees) when the pelvic rotation increased from 0 to 30 degrees. The effectiveness of the geometrical formula was shown by the consistency between the set and the calculated rotation angles of the pelvis (intraclass correlation coefficient=0.99). CONCLUSIONS: Our study provides insight into the influence of pelvic rotation on the PI, PT, and SS. PI changes with pelvic rotation. The acceptable maximum angle for reliable values of PI, PT, and SS was 17.5 degrees, and the rotation angle of the pelvis on a lateral spinopelvic radiograph can be calculated reliably.

A Computed Tomographic Morphometric Study of the Pediatric Occipital Bone Thickness: Implications for Pediatric Occipitocervical Fusion.

STUDY DESIGN: This study is a computed tomographic-based morphometric analysis of the pediatric occipital bones as related to pediatric occipitocervical fusion. OBJECTIVE: To quantify reference data concerning the thicknesses of the immature occipital bones to guide the pediatric occipitocervical fusion. SUMMARY OF BACKGROUND DATA: To the best of our knowledge, no published study has provided insight into the thicknesses of pediatric occiputs with different age groups. METHODS: 80 pediatric patients were divided into 4 age groups, and their occiputs were studied on Philips Brilliance 256 iCT scan. RESULTS: The mean thickness ± standard deviations of the pediatric occipital bones with different age groups is shown. The median and the paramedian regions are always thicker than the more lateral regions at each age group and the thickest point in the occiputs is mostly at the external occipital protuberance. The mean thickness of occiputs showed an obvious significant difference between each 2 age groups and no significant difference between male and female in different age groups except the group 4. CONCLUSION: Our investigation provides insight into the anatomy of occiputs in pediatric population and preoperative CT evaluation must be required to further decrease the risk of occipitocervical fusion.